1. Field of the Invention
The present disclosure relates to liquid crystal display technology, and more particularly to a pixel cell circuit of compensation feedback voltage.
2. Discussion of the Related Art
LCDs typically are characterized by attributes including thin, power-saving, and low radiation, and thus have been widely adopted by electronic devices, such as liquid crystal televisions, mobile phones, personal digital assistant (PDA), digital cameras, and monitors for computers and notebooks. The LCD is dominant in the flat display field.
Currently, LCDs are mainly backlight type, which may include a housing, a liquid crystal panel and a backlight module arranged within the housing. The liquid crystal panel is the key component of the LCD. However, the liquid crystal panel needs the light source provided by the backlight module to display images.
The liquid crystal panel usually includes a color filter (CF), a Thin Film Transistor Array Substrate (TFT Array Substrate), and a liquid Crystal Layer between the two substrates. Pixel electrodes and common electrodes are arranged at internal surfaces of the two substrates facing toward each other. The alignment of the liquid crystal molecules may be changed by applying the voltage to the liquid crystal molecules such that the light beams from the backlight module are reflected to generate the images. The array substrate may include a plurality of pixels arranged in a matrix. Each of the pixels includes Thin Film Transistor (TFT) to control the voltage of the pixel electrode so as to change the rotating angle of the liquid crystal. As such, the density of the optical field may be controlled.
There are a variety of structures of the TFTs. Currently, most of the LCDs adopt bottom-gate structure. The gate and the source/drain are overlapped in the bottom of the TFT, and parasitic capacitance (Cgs) may be generated in the overlapped area.
FIG. 1 is a circuit diagram of the conventional pixel cell circuit. The pixel cell circuit includes the TFT (T1). The gate of the TFT (T1) electrically connects with the scanning line G(m) corresponding to row of the pixel cell, the source of the TFT (T1) electrically connects with the data line D(n) corresponding to the column of the pixel cell, and the drain electrically connects with the pixel electrode (P). Two ends of the parasitic capacitance (Cgs) electrically connects with the gate and the drain of the TFT (T1). One end of a storage capacitance (Cst) electrically connects with the drain of the TFT (T1), and the other end of the storage capacitance (Cst) connects with a constant voltage. One end of the liquid crystal capacitor (Clc) electrically connect to the drain of the TFT (T1), and the other end of the liquid crystal capacitor (Clc) connects with the constant voltage.
The voltage of the pixel electrode (P) may be interfered by the level of the gate of the TFT (T1) due to the parasitic capacitance (Cgs). Also referring to FIG. 2, when the pixel electrode (P) has been charged fully, the level of the gate of the TFT (T1) is pulled down instantly. The voltage of the pixel electrode (P) may also be pulled down due to the capacitance coupling effect. As such, one feedthrough voltage (Vft1) is generated, and the magnitude of the feedthrough voltage (Vft1) may be represented by the equation below:Vft1=(Vgh−Vgl)×Cgs/Ctotal
Wherein Vgh represents the high level of the scanning signals transmitted by the scanning line G(m), Vgl represents the low level of the scanning signals transmitted by the scanning line G(m), Ctotal represents a sum of the capacitance connected by the pixel electrode (P), including the liquid crystal capacitor (Clc), the storage capacitance (Cst), and the parasitic capacitance (Cgs).
The voltage of the positive and negative frames of the pixel electrode (P) may be affected by the parasitic capacitance (Cgs), which results in asymmetric voltage of the positive and negative frames. This may cause problems such as flicker and image sticking, and thus the display performance may be affected. In addition, the RC delay with respect to different areas of the panel may also cause the difference of the feedback voltage. This may result in non-uniform voltage of the common electrode (Vcom), and may cause serious flicker.